Wireless communication systems employ power amplifiers for increasing the power of radio frequency (RF) signals. In a wireless communication system, a power amplifier forms a portion of the last amplification stage in a transmission chain before provision of the amplified signal to an antenna for radiation over the air interface. High gain, high linearity, stability, and a high level of power-added efficiency are characteristics of a desirable amplifier in such a wireless communication system.
In general, a power amplifier operates at maximum power efficiency when the power amplifier transmits close to saturated power. However, power efficiency tends to worsen as output power decreases. Recently, the Doherty amplifier architecture has been the focus of attention not only for base stations but also for mobile terminals because of the architecture's high power-added efficiency over a wide power dynamic range. The high efficiency of the Doherty architecture makes the architecture desirable for current and next-generation wireless systems.
RF power amplifiers use fast on and off switching for Time Division Duplexing (TDD). In addition, the RF baseband signal is bypassed to ground at an RF power amplifier's bias voltage input. Current amplifier designs often employ large RF bypass capacitors for this purpose, which prevent unwanted spurious modulation of the RF signal. However, such RF bypass capacitors may require large current charging surges to bias the RE amplifiers on and off. Newer RF power amplifier applications, such as those used in multiple-input, multiple-output (MIMO) systems, would be better served by faster switching and lower power consumption than is achievable with designs that utilize large RF bypass capacitors that need to be charged and discharged using conventional methods.
In view of the above, there is a need for improved amplifiers and related methods of operation that address one or more of the above concerns, or other concerns, associated with conventional amplifiers, and/or provide one or more advantages by comparison with conventional amplifiers.